The former detective sergeant with more than 20 years experience, was in charge of the Northland organised crime unit, which focused mainly on investigating and prosecuting drug crimes. During that time he stole the drugs to supply an informant, who's name is suppressed, and in turn received thousands of dollars.

Failure to prosecute two significant Northland drug dealers is just one of a catalogue of lingering effects on Whangarei police from ex-cop Michael David Blowers' crimes.

Speaking at Whangarei's police station Northland District Commander Superintendent Russell Le Prou said Blowers' colleagues had taken his crimes "personally".

"Each officer will have their own thoughts and feelings but at the end of the day we can agree that its hurts when someone like this is convicted."

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SENTENCED: Michael David Blowers

The drug exhibits Blowers stole from police storage were replaced with rock salt and as a result of the evidence tampering police couldn't prosecute two significant drug dealers the meth had been seized from.

Detective Inspector Stuart Allsopp Smith, who lead the investigation into Blowers' crimes, said that trial had "fallen over" because of Blowers and that local police would have felt "betrayed" that their hard work had gone to waste.

In the High Court at Whangarei today Justice Geoffrey Venning said Blowers' excuse that gang members had threatened his family didn't stack up, and this afternoon Superintendent Le Prou agreed.

"Mr Blowers would have known full well he had avenues that offered him protection and he clearly didn't avail himself of that."

The second sentencing of a corrupt police officer in a week prompted Police Commissioner Mike Bush to assure New Zealanders there was "little tolerance" for constabulary staff who fail to uphold the law.

"Cases such as these are extremely rare and they let down the 12,000 police staff who do a fantastic job each and every day," he said today.

Blowers' case follows on the heels of the sentencing of former Waitakere Constable Peter Pakau who was jailed for a raft of dishonesty and drug offences on Friday.

The Blowers and Pakau cases both involved former police officer whose liaisons with gangs and informants got them in trouble with the law.

At Pakau's sentencing in the High Court at Auckland the court was told he'd been manipulated by associates, many of them gang members, rather than being motivated by any financial gains.

New Zealand Police Association president Greg O'Connor said it was common for gangs to try and manipulate police officers and that lines could often be blurred when it came to using informants.

"It's a dangerous area, fraught with complications," he said.

"Gangs (try and manipulate) all the time. They will report back with any interactions they've had with police officers. They do their own intelligence. They know who they're dealing with, they know the good ones and the vulnerable ones.

"Police are their biggest threat to their business so of course they know a lot about them."

O'Connor said stretched police resources meant officers weren't supervised as often as they should be, particularly when they were already trusted members of the constabulary.

However Bush said there was no evidence of gangs targeting police and that it wasn't an excuse for staff who let "themselves, their colleagues and the public down".